Roller bearings such as double-row spherical roller bearings are used in various applications and are preferably designed to accommodate axial forces as well as radial forces. Roller bearings of this type typically include a plurality of rollers disposed between an outer ring (raceway) and an inner ring (raceway), and a flange or loose guide ring is provided for guiding the rollers. During operation, the rollers contact the outer ring, the inner ring, and the flange or guide ring. This contact produces friction forces between the rollers and the raceway surfaces. The tendency of the rollers to assume an equilibrium position causes the rollers to assume a certain angle relative to the rolling direction, referred to as the skew angle. This results in undesirable sliding of the rollers in a direction generally parallel to the roller axis.
The skew angle is defined as the angle between the axis of rotation of the roller and a plane normal to the path of relative motion of the raceway which confronts the rollers. This skew angle imparts to the roller surface a sliding velocity component in the axial direction at its contact with the raceway surfaces. As a result, an axial friction force will act on the inner and outer raceways and the rollers. If the direction, or sign, of the skew angle changes, the directions of the axial friction forces will change at the roller/raceway contacts.
The skew angle is defined as being positive when the friction force components acting on the roller in the axial direction are so directed that they add to or are co-directional to the axial component of the normal contact force acting on the roller at the same contact. The skew angle is also defined to be positive when the friction force components on a raceway in the axial direction are so directed that they counteract the axial load component of the external load acting on the raceway.
In many known types of roller bearings, the rollers tend to assume a negative skew angle in which the axial component of the friction forces arising in a contact zone between the rolling element and the raceway, and acting on the raceway is directed in a manner that adds to the external axial load acting on the ring. It has been determined that negative skew angles result in undesirable higher friction losses and lower bearing life than corresponding positive skew angles, particularly when the bearing load conditions contain substantial axial components. Thus, a roller bearing in which the skew angle of the rollers is controlled so as not to be excessively negative is highly desirable.